1. Field of the Invention
The present invention relates to a fuel cell formed by stacking an electrolyte electrode assembly and a metal separator in a form of a corrugated plate. The electrolyte electrode assembly includes a pair of electrodes, and an electrolyte is interposed between the electrodes. A reactant gas flow field as a passage of a fuel gas or an oxygen-containing gas, and a coolant flow field as a passage of a coolant are formed on both surfaces of the metal separator.
2. Description of the Related Art
For example, a solid polymer electrolyte fuel cell employs an electrolyte membrane. The electrolyte membrane is a polymer ion exchange membrane. The electrolyte membrane is interposed between an anode and a cathode to form a membrane electrode assembly (MEA). The membrane electrode assembly is sandwiched between a pair of separators to form a unit cell for generating electricity. In use, normally, a predetermined number of unit cells are stacked together to form a fuel cell stack.
In the fuel cell as described, a fuel gas flow field is formed in a surface of one separator facing the anode for supplying a fuel gas to the anode, and an oxygen-containing gas flow field is formed in a surface of the other separator facing the cathode for supplying an oxygen-containing gas to the cathode. Further, a coolant flow field is formed between the separators for supplying a coolant along surfaces of the separators.
In the case where metal separators are used as the separators, by providing grooves as the fuel gas flow field on one surface of the metal separator facing the anode, ridges as the back side of the grooves are formed on the other surface of the metal separator. Further, by forming grooves as the oxygen-containing gas flow field on one surface of the metal separator facing the cathode, ridges as the back side of the grooves are formed on the other surface of the metal separator.
For example, a fuel cell separator is disclosed in Japanese Laid-Open Patent Publication No. 08-222237. As shown in FIG. 14, the fuel cell separator includes a separator plate 1 and a separator frame 2. The separator plate 1 is made of metal, and bosses and dimples are formed on the separator plate 1. Specifically, a large number of projections 3, 4 are formed on the front and back surfaces of the separator plate 1 at intervals of several millimeters. When a fuel cell stack is assembled, the top portions of the projections 3, 4 tightly contact unit cells 5. A fuel gas flow field 6 and an oxygen-containing gas flow field 7 are formed between the separator plate 1 and the adjacent unit cells 5. The fuel gas flow field 6 is formed by the projections 3 of the separator plate 1, and the oxygen-containing gas flow field 7 is formed by the projections 4 of the separator plate 1.
In the above separator plate 1, the fuel gas flow field 6 is formed by a large number of the projections 3, and the oxygen-containing gas flow field 7 is formed by a large number of the projections 4. Therefore, the water produced in the power generation tends to be retained between the projections 3 or between the projections 4. At this time, since the fuel gas and the oxygen-containing gas flows between the projections 3 and the projections 4 around the water produced in the power generation reaction, the water may not be discharged smoothly. Therefore, the flows of the fuel gas and the oxygen-containing gas are inhibited, and the power generation performance is poor.
Further, in the case where water is introduced into the fuel cell stack from the outside, the water is retained, and cannot be discharged smoothly. Therefore, the power generation performance is degraded.